Not Applicable.
The present invention relates to an interlayer placed on cracked roads to repair them. More specifically, this interlayer includes a mixture of aggregate and preferably polymer modified asphalt that is used to delay or stop the occurrence of cracking, control crack severity, reduce overlay thickness, and enhance waterproofing capabilities.
When pavements deteriorate, they may be overlaid with hot mix asphalt (HMA) to repair them. When designing an overlay, the rate of crack propagation through the overlay, the rate of deterioration of the reflective crack, and the amount of water that can infiltrate through the cracks must be considered. One disadvantage with such HMA overlays is that cracks in the old pavement reflect through the new overlay. To relieve this reflective cracking, thicker overlays must be placed. Another disadvantage with such HMA overlays is that they are permeable allowing water to enter the base. A third disadvantage with these overlays is that they typically have a low strain tolerance and a low resistance to reflective cracking.
Asphalt binders which display the ability to undergo creep or stress relaxation at low temperatures in order to minimize the potential for thermal and reflective cracking may be created. The disadvantage with such binders is that they are highly ductile, and thus, roads created with them tend to rut.
Asphalt binders with a high shear modulus that resist rutting at high temperatures may also be created. The disadvantage with such binders is that they tend to be brittle at low temperatures, and thus, roads created with them tend to crack. Typical asphalt binders formulated for pavement applications usually display either high shear modulus at high temperatures or high ductilities at low temperatures but not both.
Other reflective crack control measures that are used to rehabilitate distressed Portland Cement Concrete (PCC) pavements include placing stress-absorbing membrane interlayers (SAMI), placing grids or fabrics as an interlayer before placing HMA, break and seat of PCC, rubblization of PCC, and reconstruction. One disadvantage with these processes is that they can be expensive. Another disadvantage with these processes is that if the road is not reconstructed, it may still have cracking problems.
In order to overcome these disadvantages, an overlay that is able to slow reflective cracking without rutting and protect the pavement structure is needed. Still further, this overlay should be easy to apply and provide a smooth riding surface.
It is an object of the present invention to provide a substantially impermeable interlayer for distressed pavement so that the distressed pavement is protected from moisture.
It is a further object of the present invention to provide a system for repairing a distressed and cracked road so that existing underlying cracks are delayed from reflecting through the entire pavement including the interlayer and so that raveling and further deterioration of the cracks are prevented.
Another object of the present invention is to provide a method for slowing the deterioration of Portland Cement Concrete (PCC) pavements that are reaching the end of their design life so as to delay the reconstruction of these roadways.
The system of the present invention includes a highly strain tolerant, substantially impermeable (see FIG. 3), hot mix reflective crack relief interlayer. The interlayer includes a polymer modified asphalt binder mixed with a dense fine aggregate mixture. About 100% by weight of the aggregate should be able to pass through about a 9.5 mm sieve. The interlayer mix is designed using a fatigue test and a stability test, preferably a Flexural Beam Fatigue test and a Hveem Stability test (or rut tester) are performed. Preferably, an HMA overlay that is compatible with the interlayer, as well as the demands of local traffic, is placed over the interlayer so that a protected, smooth road surface is provided. The system of the present invention may delay the first appearance of cracks and the severity of cracks for several years compared with traditional hot mix overlays.
Additional objects, advantages, and novel features of the invention will be set forth in the description that follows and in part will become apparent to those skilled in the art upon examination of the following, or may be learned by practice of the invention.